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Sedimentalogical and stratigraphic analyses of the Lagoa Feia Formation, rift phase of Campos Basin, offshore Brazil

1988; Sociedade Brasileira de Geologia; Volume: 18; Issue: 3 Linguagem: Inglês

10.25249/0375-7536.1988252260

2177-4382

Jeferson Luiz Dias, Jorge Quintão De Oliveira, Jose Costa Vieira,

Hydrocarbon exploration and reservoir analysis

The Campos Basin is located offshore the State of Rio de Janeiro along the Southeast Brazilian Continental Margin. It comprises an approximate area of 100,00 km 2 up to 3,400 m Isobath. The Lagoa Feia Formation comprises mainly the rift phase sediments of the basin. Intense tectonic activity generated normal faulting with a preferential northeastern direction and great vertical displacement. Large basalt flows, with ages varying between 120 Ma and 130 Ma, represent the onset of the rift system forming the basement upon which Lagoa Feia formation sediments were deposited. The lack of marine fossils indicates non-marine depositional environments for this formation. The formation can be subdivided into four deposition sequences: Basal Clastic Sequence, Talc-Srevensltic Sequence, Coquinas Sequence, and Clastic-Evaporitic Sequence. Sediments of the three basal sequences are indicative of typical lacustrine environments. The presence of talc and stevensite clay-minerals, and the diagenetic assemblage of the Coquinas Sequence suggest that this lake had alkaline brackish to saline waters. Alluvial fans and their associated facies deve loped on the western border and adjacent to other highs of the basin. Sand flat and mud flat facies compose the marginal portions of the lake, while in deeper waters hydrocarbon generating shales were deposited. The Coquinas Sequence represents an expressive amount of pelecipod calcirudites, and calcarenites deposits, which now are important hydrocarbon reservoirs. An important and regionally widespread erosional unconformity separates the Coquinas Sequence of the overlying Clastic-Evaporitic Sequence, which is characterized by shallow water sedimentation defined through stromatolitic and nodular limestones associated with extensive deposition of alluvial fans. The top of the Lagoa Feia Formation is marked by a thick evaporitic layer deposited under hot arid to semi-arid climate and relative ly stable tectonic conditions, connected with the ocean at the south.